The ER model represents the logical view of a system using entities, entity types, entity sets, attributes, and relationships. An entity is an object with a physical or conceptual existence, such as a person, course, or job. Entities of the same type make up an entity set. Attributes define entity types and can be key, composite, multivalued, or derived. Relationship types represent associations between entity types, such as students enrolled in courses. Relationship sets involve one or more entity sets and can be unary or binary.

1. Introduction of
ER Model
Add a Footer
1
Dr.M.UMADEVI
ASSISTANT PROFESSOR
DEPARTMENT OF CS
SACWC
CUMBUM

2. ER Model is used to model the logical view of
the system from data perspective which consists
of these components:
Entity, Entity Type, Entity Set –
An Entity may be an object with a physical
existence – a particular person, car, house, or
employee – or it may be an object with a
conceptual existence – a company, a job, or a
university course.

3. An Entity is an object of Entity Type and set of
all entities is called as entity set. e.g.; E1 is an
entity having Entity Type Student and set of all
students is called Entity Set. In ER diagram,
Entity Type is represented as:

4. Attribute(s):
Attributes are the properties which define the
entity type. For example, Roll_No, Name, DOB,
Age, Address, Mobile_No are the attributes
which defines entity type Student. In ER
diagram, attribute is represented by an oval.

5. 1. Key Attribute –
The attribute which uniquely identifies each
entity in the entity set is called key
attribute.For example, Roll_No will be unique
for each student. In ER diagram, key attribute is
represented by an oval with underlying lines.

6. 2. Composite Attribute –
An attribute composed of many other
attribute is called as composite attribute. For
example, Address attribute of student Entity
type consists of Street, City, State, and Country.
In ER diagram, composite attribute is
represented by an oval comprising of ovals

7. 3. Multivalued Attribute –
An attribute consisting more than one value for
a given entity. For example, Phone_No (can be
more than one for a given student). In ER
diagram, multivalued attribute is represented
by double oval.

8. 4. Derived Attribute –
An attribute which can be derived from other
attributes of the entity type is known as
derived attribute. e.g.; Age (can be derived
from DOB). In ER diagram, derived attribute is
represented by dashed oval.

9. Relationship Type and Relationship Set:
A relationship type represents the association
between entity types. For example,‘Enrolled in’
is a relationship type that exists between entity
type Student and Course. In ER diagram,
relationship type is represented by a diamond
and connecting the entities with lines.

10. Degree of a relationship set:
The number of different entity sets participating in a
relationship set is called as degree of a relationship set.
1. Unary Relationship –
When there is only ONE entity set participating in a
relation, the relationship is called as unary relationship.
For example, one person is married to only one person.

11. Degree of a relationship set:
The number of different entity sets participating in a
relationship set is called as degree of a relationship set.
1. Unary Relationship –
When there is only ONE entity set participating in a
relation, the relationship is called as unary relationship.
For example, one person is married to only one person.

12. 2. Binary Relationship –
When there are TWO entities set participating in a
relation, the relationship is called as binary
relationship.For example, Student is enrolled in Course.

13. THANK YOU